Precolumn inlet for chromatographs

ABSTRACT

Removable precolumn inlet apparatus for direct injection into high resolution packed or capillary columns for chromatographs. A front body and a rear body, the front body being removably attached to the rear body and contains a hot zone where evaporation of samples occur and an air-cooled zone in which sealing septums are disposed. A precolumn tube is disposed in the front body which is heated so that samples are evaporated in said tube. A separatory column of high revolving ability is operably connected to the precolumn tube, said rear body having a cavity in which a short length of the high-resolution column extends, said short length of the high-resolution column being refrigerated, there being a cold shield in the cavity to reduce the heat loss of the rear body when refrigeration is taking place. The rear body also acts as a heat source for rapidly warming up the cold zone after the sample components have been condensed on the head end of the column. The short linear dimension of the high-resolution column is subjected to refrigeration in the cavity of the rear body so as to condense the sample components and thereby provide a sharp sample injection into the continuing high-resolution column when refrigeration is turned off. The surrounding heat block of the rear body provides a large thermal mass to rapidly bring the capillary column segment back up to column temperature.

FOREIGN PATENTS 108,750 6/1964 Netherlands 73/422 (GC) Primary ExaminerS. Clement Swisher Attorney-J. Carroll Baisch ABSTRACT: Removable precolumn inlet apparatus for direct injection into high resolution packed or capillary columns for chromatographs. A front body and a rear body, the front body being removably attached to the rear body and contains a hot zone where evaporation of samples occur and an air-cooled zone in which sealing septums are disposed. A precolumn tube is disposed in the front body which is heated so that samples are evaporated in said tube. A separatory column of high revolving ability is operably connected to the precolumn tube, 73/231 said rear body having a cavity in which a short length of the 73/422 GC high-resolution column extends, said short length of the high- [51] ll. resolution column being refrigerated, there i g a cold Shield in the cavity to reduce the heat loss of the rear body when 421 refrigeration is taking place. The rear body also acts as a heat source for rapidly warming up the cold zone after the sample components have been condensed on the head end of the column.

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References Cited UNITED STATES PATENTS lnventors Carol A. M. G. Cramers La Habra, Calit; Mateus M. Van Kessel, Breukelen, Netherlands 848,372 Feb. 27, 1969 Hamilton Company Whittier, Calif. by said Van Kesel 10 Claims, 4 Drawing Figs.

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[54] PRECOLUMN INLET FOR CHROMATOGRAPHS a reao HMTNHKM 22568 6666666 9999999 lllllll l/l/ll/ 799 943 l 81mm I 33574 9 56047 2333333 United States Patent [2ll Appl. No.

[22] Filed [45] Patented July 13,197]

[73] Assignee [50] Field The short linear dimension of the high-resolution column is subjected to refrigeration in the cavity of the rear body so as to condense the sample components and thereby provide a sharp sample injection into the continuing high-resolution column when refrigeration is turned off. The surrounding heat block of the rear body provides a large thermal mass to rapidly bring the capillary column segment back up to column temperature.

lIIII'l/Illll 'Il PRECOLUMN INLET FOR CHROMATOGRAPHS BACKGROUND OF THE INVENTION This invention relates generally to the art of chromatography and relates more particularly to injector means for chromatographs. With ordinary syringe techniques, it is practically impossible to repeatedly inject sufficiently small and uniform samples for high-resolution columns.

BRIEF SUMMARY OF THE INVENTION The present invention solves the problem of repeatedly injecting very small and uniform samples for high-resolution columns.

The present invention comprises a front end or front body and a rear end or rear body, the front body being removably attached to the rear body. The front body contains a hot zone where evaporation of samples occur and an air-cooled zone in which sealing septums are disposed. A fitting is provided for connecting the inlet to a carrier gas supply. A precolumn glass tube extends longitudinally inside and is centered in the front body, evaporation of samples occurring in said tube. A cartridge heater supplies heat to both the front and rear bodies.

A separatory column of high resolving ability, e.g. capillary, packed capillary, or small-diameter packed column extends through the lower body and is operably connected to the precolumn, said lower body having a cavity in which a short length of the high-resolution column extends. This short length of the high-resolution column is adapted to be refrigerated, there being a cold shield in said cavity which reduces heat loss of the rear body when refrigeration is taking place. The rear body also acts as a heat source for rapidly warming up the cold zone after the sample components have been condensed on the head end of the column.

As used herein the term separatory column means a separatory column of high resolution. The term high-resolution column is also used herein to means such a separatory column.

A sample to be analyzed is dissolved in an excess of solvent that is sufficiently different in volatility that it will clearly separate from the sample components or may be completely retained in the precolumn. If a low-volatility solvent is used, the sample and solvent in which it is dissolved is injected into the precolumn and high temperature is used to drive the sample components from the solvent directly into the column.

If a high-volatility solvent is used both the solvent and sam ple enter the column but the solvent is rapidly eluted compared to the sample components.

The short linear dimension of the high-resolution column is subjected to refrigeration in the cavity of the rear body so as to condense the sample components and thereby provide a sharp sample injection into the continuing high-resolution column when refrigeration is turned off. The surrounding heat block of the rear body provides a large thermal mass to rapidly bring the capillary column segment back up to column temperature. Thus the proper injection of the sample can be made.

OBJECTS OF THE INVENTION It is an object of the invention to provide inlet means for chromatographs including a removable precolumn inlet for direct injection into high-resolution packed or capillary columns.

It is another object of the invention to provide apparatus for direct injection of a sample dissolved in a suitable solvent which is retained within the inlet on a very small precolumn. Usually this precolumn is packed with inert support material. However, should a high-volatility solvent be used both the solvent and sample enter the column but the solvent is rapidly eluted compared to the sample components.

It is still another object of the invention to provide a refrigeration system to trap a sample which is spread over too big a volume or too long a time of injection. The sample is trapped inside the top of the high-resolution column in a narrow zone and then released quickly.

The characteristics and advantages of the invention are further sufficiently referred to in connection with the following detailed description of the accompanying drawings which represent one embodiment. After considering this example skilled persons will understand that many variations may be made without departing from the principles disclosed and we contemplate the employment of any structures, arrangements or modes of operation that are properly within the scope of the appended claims.

Referring to the drawings, which are for illustrative purposes only:

FIG. 1 is a longitudinal sectional view through apparatus embodying the invention;

FIG. 2 is a view taken from line 2-2 of FIG. 1;

FIG. 3 is a sectional view taken on line 3-3 of FIG. 1; and

FIG. 4 is an alternative arrangement for connection of the precolumn and capillary column together.

Referring more particularly to FIG. 1, there is shown a front body, indicated generally at 10, and a rear body, indicated generally at 12.

The front body is of stainless steel although it may be of any other suitable material. It comprises a cylindrical main body portion 14 having substantial mass, there being an annular radially outwardly extending flange 16 at one end.

At the other end of the body portion 14 there is an axially or longitudinally extending neck 18 terminating in an enlarged part 20 having a plurality of longitudinally spaced annular cooling fins 22 thereon. There is a bore 24 extending from the free end of the part 20 which has a counterbore 26 at the outer end, said counterbore being tapped. The bore 24 and counter bore 26 are connected together by a flaring shoulder 28.

A radial or cross bore 30 extends from the bore 24 to an enlarged, tapped bore 32 into which an externally threaded end portion of a carrier gas tube 34 is screwed, a fitting 36 being operably attached to the free end of said tube 34.

At the end of the body 10 having the flange 16 there is an axially or longitudinally extending externally threaded boss 38 and a bore 40 extends longitudinally in the body from the free or outer end of the boss 38, said bore 40 terminating short of the bore 24 but being connected therewith by a reduced diameter bore 42, there being a shoulder 44 at the junction of the bore 40 and bore 42. Bore 40 is of just enough greater diameter than that of a tubular precolumn sleeve 48 within which a precolumn or precolumn tube 49 is disposed. The outer end of the sleeve 48 abuts against the shoulder 44 but the adjacent end of the precolumn tube extends outwardly in the bore 42, terminating at the inner end of the bore 24.

At its end opposite shoulder 44 the sleeve 48 extends to the free end of the boss 38. The inside diameter of sleeve 48 is such as to snugly receive the precolumn but while permitting the precolumn to be slidably inserted into and out of said sleeve. The same is true of the fit of the precolumn in the bore 42. The end of the sleeve 48 at the boss 38 has a counterbore 50 the purpose of which will be described hereinafter, there being a shoulder 51 at the inner end of said counterbore.

Body part 14 has a longitudinally extending bore 54 parallel to but spaced outwardly of the axis of the body 10 and in which is operably disposed an electric heater or cartridge heater 56 having wires 58 for connection with a source of electric power.

There is means for cooling the fins 22 with a suitable gas, air

being one such gas. This means comprises a tube 60 adapted to be connected with a source of air under pressure by a tubing fitting 62. A portion 64 of tube 60 extends through aligned openings 66 in the fins 22 adjacent their peripheries and the portion 64 of tube 60 has a plurality of air discharge openings 68 therein located to discharge cooling air between the fins. The tube portion 64 is s secured in holes 66 by any suitable means such as, for example, brazing, welding or the like.

A septum holder 74 of slightly smaller diameter than the diameter of bore 24 is disposed in the bore 24. At its inner end the septum holder has a recess 76 in which a precolumn septum 78 is disposed, recess 76 being shallower than the thickness of the septum '78 so that the latter extends forwardly of the septum holder and abuts against the inner end wall of the bore 24. The adjacent end of the precolumn extends through the precolumn septum 78 which forms a seal thereabout.

At its opposite or outer end the septum holder 74 has a recess 80 at the inner end of which is disposed a needle sep tum 82 and a compression washer $41 at the outer side or" the needle septum, said washer having a central hole therethrough. The outer end of septum holder "74 terminates adjacent the shoulder 28 and there is an O-ring engaging said shoulder 28 and the outer end of the septum holder '74.

Means for releasably retaining the septum holder and the septums therein in the bore 24 is provided and comprises a seal screw, indicated generally at 90, said seal screw having a body part 92 with external screw threads 9d thereon and a forwardly or inwardly extending reduced diameter part 96, there being a shoulder 98 at the junction of the reduced diameter part 96 and the body part 92. At its outer end the seal screw has a knurled heat Hill. Shoulder 98 engages the -ring 86 and the inner or free end of the reduced diameter part en gages the compression washer 34 so that by tightening the seal screw the septums are suitably compressed and the O-ring seals the outer end of the bore 24.

Septum holder 74 has a longitudinally or axially extending passage H02 therethrough and a plurality of cross bores ltl i adjacent the inner end of the septum holder, said cross bores being of somewhat larger diameter than the axially extending bore. The outside diameter of the septum holder is sulficiently smaller than the diameter of the bore 24 to permit carrier gas, introduced by way of the carrier gas tube 34 and passage or bore to enter the cross bores.

The rear body 12 is of aluminum although it may be of any other suitable material. It is of substantially the same outside diameter as the front body and includes a main body 3039 which has radially outwardly extending annular flanges H0 and 112 at the outward and forward ends respectively. There are openings in the outward lllill flange aligned with tapped bores, not shown, in the flange 16 of the front body for reception of screws lllil whereby the bodies are secured together. The flange M2 also has openings therein for reception of screws 1116 whereby the apparatus is removably attached to a chromatograph.

The main body portion is cylindrical and of substantial mass and has a recess 12%) at the end adjacent the front body R0 for reception of the boss 38 of the front body. The rear body is usually held at column temperature, whereas the front end part is maintained at a higher temperature to provide rapid vaporization of the sample from the solvent. At the opposite end there is a projection 1122 extending axially outwardly for operable connection with the chromatograph instrument.

A bore i124 extends axially or longitudinally of the rear body from the free end of the projection ll22 to the recess 1249, the bore 124 being of such size as to snugly but slidingly receive a capillary tube or packed column 126 so that this column can be inserted into said bore K24 and removed therefrom. The high resolution or separatory column 126 is an outer end portion of the separatory column of high resolution of the chromatograph and extends from the forward or free end of the projection 1122 through an opening 128 in the end wall 130 of a nut 132 which is screwed onto the externally threaded boss 38.

At the outer end of the boss 38 there is disposed a washer R34 of suitable material, one such material being Teflon" which is the registered trademark of the duPont Company for their fluorocarbon resins. Washer 134 has an axial opening therethrough in which the high-resolution (capillary or smalldiameter packed) column ll2t5 is snugly received and through which said column R26 extends, said column extending into the counterbore 50 of the precolumn sleeve 4?. The end of the high-resolution column in the counterbore 5th abuts against the shoulder 51! with the passage through said higl'r-IESDlUtiO'fl column in alignment and register with the passage through the prccolumn. The adjacent ends of the high-resolution column and the precolumn are in tight abutment with each other.

At the outer side of the washer B34- is a compression washer 13d of any suitable resilient material such as plastic or the like having an opening Mil therethrougli aligned with the opening in the washer llIi-i, said opening 1140 being larger than the opening in the washer 1134. Washers 134 and 138 are compressed between the free end of the boss 3% and the wall oi the out when said nut is tightened on the boss 38 whereby the washer B34 is compressed tightly about the high-resolution column extending through the opening in said washer R34 to prevent escape of fluid about said column at this point. Thus a seal is provided for the high-resolution column and the adjacent ends of the precolumn and high-resolution column are held securely in abutting position so that there is a completely glass defined passage from the sample injection to the chromatograph. in other words there is an all glass inlet.

The rear body l2 has a longitudinally extending recess or bore M 1.- for operably reception of an end portion of the cartridge heater or heating element at which projects from the adjacent end of the from body ND. The bore 1144 is also spaced from the axis of the rear body but parallel thereto. A second electric heating element, indicated at MS, is disposed in a bore 156! in the rear body 32, bore being offset or spaced from the axis of the rear body and parallel thereto. Heater element 1148 has means for connection with a source of electric power, said means comprising wires 152.

Refrigeration means is provided for refrigerating a short linear section or segment of the high resolution, said means comprising a transverse or cross bore 160 having means for connecting same with a source of a gas that will create a substantial lowering of the temperature in a cold zone and which can be considered a cold trap. Liquid carbon dioxide has been found to be a very satisfactory gas for refrigerating the short section of the high-resolution column and means for connecting the cross bore 16% with a source of such gas comprises a conduit H32 controlled by an open-close valve V that can start and stop the jetting of the CO to the cold zone. Conduit 162 is connected to a jet i163 adapted to discharge liquid CO into the interior chamber B65 of a cold shield i166 which is disposed within the cross bore Md and which comprises a generally rolled piece of metal such as stainless steel or other suitable materialv The shield is somewhat flattened and there is a hole through the roll of metal through which the high resolution column 112d extends, the shield loo being supported on the high-resolution column so that the shield does not come in contact with the wall of the cross bore. When the liquid CO is discharged into the chamber of the shield it is discharged directly onto that portion of the high resolution column which extends through the chamber 165.

Preparatory to sample introduction the sample may be dissolved in an excess oi volatile or nonvolatile solvent. Various well-known solvents may be used but it will be sufficient to describe the use of silicone oil as an example of a nonvolatile solvent. The solvent used should be chosen such that it is clearly separable from the sample components and may even be completely retained in the precolumn.

The solvent with the sample dissolved therein is injected into the precolumn with a syringe of suitable well-known type. The needle of the syringe is inserted into an axial passage, not shown, through the seal screw 9% provided for this purpose and through the central opening, not shown, in the compression washer 843 and thence through the needle septum 82 which is self-sealing when the needle is withdrawn. The needle is also pushed into the precolumn at its opening in space 104. When the prccolumn has packing or support material 170 therein the needle is inserted into the precolumn so that the free end of the needle is adjacent to the packing. Various wellknown inert support materials may be used. The solvent with the dissolved sample components therein is then injected into the precolumn.

The heating element 3% is energized well before injection of samples and maintains a high temperature in the front body 50 so that the sample components are rapidly driven from the solvent as it enters the precoiurnn. The sample components are carried by the carrier gas directly into the open end of the higl'i-resolution or capillary column.

Should a high-volatility solvent be used both the solvent and sample enter the column but the solvent is rapidly eluted compared to the sample components.

Further, provision is made to minimize band spreading of the sample at the end of the high-resolution column. This is effected by means of the refrigeration cold trap or a refrigerated cold zone where the sample is condensed, the sample components being later released as a narrow sample plug.

In order to effect refrigeration a suitable gas is used. Carbon dioxide has been found to be highly satisfactory for this purpose and will be used as an example, it being understood that other cooling agents may be used such as air, N etc.

With carbon dioxide as the example of a suitable cooling agent, the valve V is opened so that the CO jet discharges the liquid carbon dioxide onto the short linear section of the highresolution column extending through the chamber 165 of the cold shield in the cross bore 160. Expansion of the CO in the cross bore or refrigeration chamber 160 causes a drop in the temperature in said cross bore 160 and in the temperature of the cold shield 166 and consequently in the temperature of the short section of the high-resolution column extending through the shield I66 and cross bore 160. This section may be about three-tenths of an inch in linear dimension or any other suitable length. When the sample components previously evaporated in the capillary precolumn have been condensed the valve V is turned off so that there is a sharp band injection of the sample into the continuing high-resolution column at the time the CO jet is turned off.

As soon as the valve V is closed and the CO jet is turned off, the surrounding heat block of the lower body provides a large heat source which rapidly brings the short linear portion of the high-resolution column back to column temperature. The cold shield is spaced away from the lower body to keep the refrigeration characteristics of the expanding carbon dioxide isolated to the tiny segment of the high-resolution column subjected to refrigeration within the shield 166. As soon as this tiny or short portion of the high-resolution column is heated up the narrow sample plug passes through the portion of the high-resolution column between the bore 160 and the free end of the projection 122 and thence into the chromatograph.

The part 20 of the front body may be considered a septum housing. This housing must be kept colder than the precolumn chamber or passage 40 in the body portion 14, the reason being that the precolumn chamber has to be hot enough to evaporate the sample from the solvent but that temperature is frequently too high for the mechanical survival of the septum. The finned top body part provides means for cooling to maintain the lower temperatures fo the septums when referenced to the hot precolumn body 14.

The external air supply provides adequate cooling by forced airflow across the cooling fins to maintain an adequate temperature gradient between the septum housing and the precolumn. A further aid in maintaining this temperature gradient is provided by the narrow or small dimensions of the connecting metal between the radiating fins of the from body part 20 and the bulk of the metal around the hot precolumn.

Referring to FIG. 4 an alternative connecting means between the precolumn and the high-resolution column is shown. In this arrangement the sleeve 48 has a flaring end portion 176 in which the adjacent end of the high-resolution column 126 is received. At its narrowest point or throat 178 the flaring end portion is of smaller inside diameter than the outside diameter of the high-resolution column so that the latter is tightly wedged in said flaring end portion 176.

it is to be understood that the high-resolution column may be a capillary or high-resolution packed column.

In the case of a nonvolatile solvent the precolumn sample is separated by retaining the solvent therein. An additional possible way to use the inlet is to concentrate trace components by refrigeration from the samples normally too large to be handled by high-resolution columns without refrigeration.

The precolumn can be used empty or packed with any suitable support. catalyst, etc.

When the precolumn is not packed or is left out, the inlet can be used for "on column" injections where the columns are less than or equal to one-eighth inch O.D.

Packed precolumns can also be used as replaceable filters for the samples to trap any nonvolatile residue of the samples.

With reference to the needle septums, it is to be understood that these are self-sealing and may be of any suitable character. One type of such self-sealing septums is disclosed in the McKinney application for a SEPTUM, Ser. No. 496,337, filed Oct. I4, 1965 and assigned the Hamilton Company, the assignee of the present application. The precolumn septum 78 may also be of this type.

We claim:

1. An inlet for chromatographs comprising:

A. elongated generally tubular body means;

8. elongated passageway means having inlet and outlet ends in said body means, a high-resolution column having inlet and outlet means arranged in one end portion thereof;

C. a precolumn having inlet and outlet means arranged in the other end portion of said passageway means in alignment with said high-resolution column and the outlet end of said precolumn being operatively connected to the inlet end of said high-resolution column for delivering gas directly thereinto;

D. means in and for heating said body means;

E. self-sealing septum closing means in one end of said body means for sealing the inlet end of said passageway means and through which a sample is injected into said precolumn;

F. means for introducing carrier gas into one end portion of said body means and into the inlet end of said precolumn;

G. cooling means in a short linear section of said highresolution column for condensing the sample components in said section as a narrow sample plug.

2. The invention defined by claim 1, wherein said cooling means comprises a refrigerating chamber through which the high-resolution column extends and in which said short linear section is disposed; a metal shield in said chamber, said shield being disposed on part of said linear section of the high-resolution column within said cold trap; and means for jetting a gas into said chamber for creating a relatively low temperature as said gas expands and flows through said chamber.

3. The invention defined by claim 1, including a second heater for heating that portion of the body means in which the high-resolution column extends.

4. The invention defined by claim 1, wherein the body means has a septum chamber at the end having the inlet end of the precolumn.

5. The invention defined by claim 4, wherein a portion of the body means about the septum chamber is of reduced diameter, and there are longitudinally spaced, radially extending fins on the reduced-diameter part of the body means, and means for jetting cooling air on said fins.

6. The invention defined by claim 4, wherein a portion of the precolumn inlet end extends into the septum chamber; a precolumn seal on said precolumn inlet end portion; and a self-sealing needle septum in said septum chamber operably mounted outwardly of the precolumn septum.

7. The invention defined by claim 6, including a septum holder having recesses for the respective precolumn septum and needle septum.

8. The invention defined by claim 7, including a seal screw threadably disposed in an outer end portion of said septum chamber for exerting compressive force on said septums.

9. The invention defined by claim 1, wherein the body means comprises a rear body and a front body, said bodies being of relatively large mass; there being means for removably securing said bodies together.

10. The invention defined by claim 9, wherein A. the passageway means extends longitudinally in each of said bodies, said passages being in longitudinal alignment with each other;

B. the high-resolution column being in the passage of the rear body and having its inlet end therein;

C. the precolumn being in the passageway means of the front body;

D. the means for operably connecting the outer end of said precolumn to the open inlet end of the high-resolution column;

E. a heater disposed in both of the bodies for heating same;

F. a second heater in the rear body;

G. a cold trap in the rear body for refrigerating a short linear section of the high-resolution column in said rear body;

H. the front body having a reduced-diameter part at the inlet end of the precolumn, said reduced-diameter part having a septum chamber into which an outer end part of the precolumn extends;

l. a precolumn septum disposed on said outer end part of 

2. The invention defined by claim 1, wherein said cooling means comprises a refrigerating chamber through which the high-resolution column extends and in which said short linear section is disposed; a metal shield in said chamber, said shield being disposed on part of said linear section of the high-resolution column within said cold trap; and means for jetting a gas into said chamber for creating a relatively low temperature as said gas expands and flows through said chamber.
 3. The invention defined by claim 1, including a second heater for heating that portion of the body means in which the high-resolution column extends.
 4. The invention defined by claim 1, wherein the body means has a septum chamber at the end having the inlet end of the precolumn.
 5. The invention defined by claim 4, wherein a portion of the body means about the septum chamber is of reduced diameter, and there are longitudinally spaced, radially extending fins on the reduced-diameter part of the body means, and means for jetting cooling air on said fins.
 6. The invention defined by claim 4, wherein a portion of the precolumn inlet end extends into the septum chamber; a precolumn seal on said precolumn inlet end portion; and a self-sealing needle septum in said septum chamber operably mounted outwardly of the precolumn septum.
 7. The invention defined by claim 6, including a septum holder having recesses for the respective precolumn septum and needle septum.
 8. The invention defined by claim 7, including a seal screw threadably disposed in an outer end portion of said septum chamber for exerting compressive force on said septums.
 9. The invention defined by claim 1, wherein the body means comprises a rear body and a front body, said bodies being of relatively large mass; there being means for removably securing said bodies together.
 10. The invention defined by claim 9, wherein A. the passageway means extends longitudinally in each of said bodies, said passages being in longitudinal alignment with each other; B. the high-resolution column being in the passage of the rear body and having its inlet end therein; C. the precolumn being in the passageway means of the front body; D. the means for operably connecting the outer end of said precolumn to the open inlet end of the high-resolution column; E. a heater disposed in both of the bodies for heating same; F. a second heater in the rear body; G. a cold trap in the rear body for refrigerating a short linear section of the high-resolution column in said rear body; H. the front body having a reduced-diameter part at the inlet end of the precolumn, said reduced-diameter part having a septum chamber into which an outer end part of the preColumn extends; I. a precolumn septum disposed on said outer end part of the precolumn; J. a needle septum operably mounted in said septum chamber in outwardly spaced relation to the precolumn septum; K. means for putting said septums under compression, said means having a passage therein for reception of a needle, said passage being aligned with the precolumn; L. a plurality of longitudinally spaced radial fins on said reduced-diameter part; M. means for jetting air onto said fins; N. and means for introducing a carrier gas to the inlet end of said precolumn. 